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(meteorobs) Meteor Activity Outlook for May 25-31, 2001
The last week of the month will still be a good one for meteor observers
as the moon is limited to the evening sky and will set before the prime
late morning hours. The estimated total hourly rates for evening
observers this week should be near 1 for those in Northern Hemisphere
and 2 for Southern Hemisphere observers with some interference from the
moon. For morning observers the estimated total hourly rates should be
near 7 for the Northern Hemisphere and 11 for those located in the
Southern Hemisphere. These rates assume that you are watching from rural
areas away from all sources of light pollution except for the moon. The
actual rates will also depend on factors such as personal light and
motion perception, local weather conditions, alertness and experience in
watching for meteor activity. The positions listed below are exact for
Saturday night/Sunday morning May 26/27. The positions do not change
greatly day to day so these positions may be used during this entire
period.
The Antihelion radiant is now located at 17:20 (260) -23. This area of
the sky is located in southeastern Ophiuchus just 2 degrees north of the
the 3rd magnitude star Theta Ophiuchi. Any slow to medium speed meteor
from northern Scorpius, southern Serpens Cauda, northwestern
Sagittarius, or southern Ophiuchus may be a good candidate for this
shower. This area of the sky is best placed near 0200 local daylight
time (0100 local standard time) when it lies on the meridian. At this
time expect to see perhaps 1 per hour from locations in the Northern
Hemisphere and 2 meteors per hour from the Southern Hemisphere. Unlike
most of the annual showers the antihelion radiant is produced by debris
from unknown sources orbiting in a direct motion like the earth. These
sources are most likely asteroids, which produce stony and metallic
debris whose density is much greater that produced by comets. This
debris collides with the earth on the inbound portion of its orbit,
before its closest approach to the sun. Therefore we best see them just
after midnight when we are facing the direction from which this activity
appears. The antihelion radiant is active all year from an area of the
sky nearly opposite that of the sun. The radiant will travel
approximately one degree eastward per day and travels through many
different constellations over the course of a year. It is easiest to
simply list these meteors as "ANT" but a majority of meteor
organizations prefer that you list them from the constellation in which
the radiant is currently located or the constellation where the shower
reaches maximum activity. For instance those who share reports with the
IMO should now label these meteors as Sagittarids (SAG).
The Beta Corona Australids are listed among the radiants of the Dutch
Meteor Society. They reached maximum activity on May 16. The current
radiant position lies at 19:52 (298) -39. This position lies in
southeastern Sagittarius 4 degrees north of the 4th magnitude star Iota
Sagittarii. Due to the low southern declination this shower is limited
to observers in the tropics and the Southern Hemisphere. The radiant
lies highest in the sky near 0430 local daylight time. ZHR's for this
shower are only 3 at maximum so don't expect to see much, if any
activity, from this radiant. This is especially true if you live north
of the equator. At 45 km/sec. members of this shower would be of medium
velocity unless seen near the radiant or the horizon.
The Northern Apex radiant is now located at 22:20 (335) +06. This
position lies in southwestern Pegasus 3 degrees east of the 4th
magnitude star Theta Pegasi. This area of the sky is best placed for
viewing during the last dark hour before dawn. Since this radiant is
diffuse any meteors from northern Aquarius, Equuleus, extreme western
Pisces, or southwestern Pegasus could be a good candidate. As seen from
the Northern Hemisphere this source should produce at least 1 meteor per
hour during the last few hours before dawn. Rates seen from the Southern
Hemisphere should be similar. Like the antihelion radiant both apex
radiants are active all year long and travel approximately one degree
eastward per day. Unlike the antihelion debris these particles orbit the
sun in a retrograde motion opposite that of the earth and are most
likely produced by unknown comets. They strike the earth after their
closest approach to the sun. Since they are moving in opposite
directions these particles strike the earth at tremendous velocities
often creating bright meteors with persistent trains. These particles
strike the earth on the morning side of earth and are best seen just
before morning twilight while the sky is still perfectly dark. There are
meteors with a zero inclination that radiate precisely from the apex
point on the ecliptic, exactly 90 degrees west of the sun. These meteors
are rare though as the earth orbits the sun it "sweeps clean" much of
the material that shares the same orbit. Much more debris is located
just north and south of the earth's orbit with slightly higher or lower
inclinations. This creates the northern and southern branches of the
apex activity. Meteors from both branches are normally included in the
sporadic count but should also be noted in some manner as to which
branch of the apex complex they appear to radiate.
The Southern Apex source lies exactly 30 degrees south of its northern
counterpart at 22:20 (335) -24. This position lies on the Pisces
Austrinus/Aquarius border some 7 degrees northwest of the bright star
Fomalhaut (Alpha Pisces Austrinis). Like the northern apex these meteors
are best seen toward dawn when the radiant lies highest above the
horizon in a dark sky. Any meteor from Pisces Austrinus, southeastern
Capricornus, northwestern Sculptor, or southern Aquarius could possibly
be a candidate from this source. As seen from the Northern Hemisphere
this source now lies so low in the southeastern sky that chances are
little or no activity will be seen. With the radiant being situated much
higher in the sky, rates seen from the Southern Hemisphere should be
better with perhaps 2-3 of these meteors being seen per hour.
The Eta Aquarids reached maximum activity on May 5. Rates are now
declining but perhaps one shower member can still be seen during the
last hour before dawn. The radiant position lies at 23:44 (356) +08.
This area of the sky is on the Pisces/Pegasus border some 3 degrees
northwest of the 4th magnitude star Omega Piscium. This shower is
difficult to see north of 45 degrees north latitude as the radiant does
not rise very high before the beginning of morning twilight. The north
and south tropical areas as well as Australia and Southern Africa enjoy
the best view of this shower. These meteors have a geocentric velocity
of 66 km/sec., which means they would appear to move slowly if seen near
the radiant or near the horizon. If seen far from the radiant and high
in the sky then they would appear to move swiftly. The Eta Aquarids
also produce a high percentage of persistent trains.
The Sporadic rates for the Northern Hemisphere are now near their lowest
levels of the year. One would expect to see perhaps 5 random meteors per
hour during the last hours before dawn from rural observing sites. This
estimate and the morning estimate for the Southern Hemisphere does not
include the apex meteors listed above. During the evening hours perhaps
1 random meteor can be seen per hour. Rates seen from the Southern
Hemisphere would now be slightly better than those seen in the Northern
Hemisphere with perhaps 6 random meteors being seen per hour during the
late morning hours and 2 per hour during the evening.
Clear Skies!
Robert Lunsford
AMS Visual Program Coordinator
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